The present invention relates in general to hydraulic machines and in particular it relates to a hydraulic axial piston engine having a rotary shaft, stationary lifting cams arranged around the shaft, and two sets of axial pistons arranged opposite each other and cooperating with respective lifting cams to drive the shaft.
The hydraulic axial piston machines of this type known from prior art have the juxtaposed pistons arranged in a common bore formed in a cylinder block which is fixedly mounted in a machine housing. The pistons cooperate with assigned lifting cams which are connected for joint rotation to a shaft and thus transform their lifting force into a rotary movement of the shaft. The feeding and the discharge of the working fluid into or from the cylindrical spaces above the pistons takes place via recesses in the shaft whereby an axial section of the periphery of the shaft together with the corresponding inner wall surface of the cylinder blocks provides for the necessary control of the admitted or discharged working fluid. The working fluid is supplied through an inlet port and discharged through an outlet port, both ports being formed in the stationary machine housing and communicate via a rotary conduit with the recesses in the shaft.
Inasmuch as it is impossible to compensate for play both in the controlling sections and in the rotary conduit, relatively high losses due to the leakage of the working oil take place and these losses are still increased in the case when the shaft bends due to the radial forces transmitted thereon. Apart from the above-described leakage losses another disadvantage of the known radial piston machines is in the fact that the control surface is limited by the periphery of the shaft and consequently the prior art control enables only a limited power control of the machines.